Plasma arc torches are widely used for the high temperature processing (e.g., cutting, welding, and marking) of metallic materials. A plasma arc torch generally includes a torch body, an electrode mounted within the body, an emissive insert disposed within a bore of the electrode, a nozzle with a central exit orifice, a shield, electrical connections, passages for cooling and arc control fluids, a swirl ring to control the fluid flow patterns, and a power supply. The torch produces a plasma arc, which is a constricted ionized jet of a plasma gas with high temperature and high momentum. Gases used in the torch can be non-reactive (e.g., argon or nitrogen), or reactive (e.g., oxygen or air).
In the process of plasma arc cutting or marking a metallic workpiece, a pilot arc is first generated between the electrode (cathode) and the nozzle (anode) within a torch. When operating in this pilot arc mode, the electrode can separate from the nozzle, forming an arc between the electrode and nozzle, e.g., as described in U.S. Pat. No. 4,791,268, the contents of which are incorporated herein by reference. The gas passing between the nozzle and the electrode is ionized to form a plasma, which then exits an exit orifice of the nozzle. The gas can be passed through a swirl ring to impart a tangential motion to the gas as it passes through the torch, thereby improving torch performance. When the torch is moved near a workpiece, the arc contacts the workpiece and the current return path then transfers from the nozzle to the workpiece. Generally, the torch is operated in this transferred plasma arc mode, which is characterized by the flow of ionized plasma gas from the electrode to the workpiece, with the current return path being from the workpiece back to the power supply. The plasma thus generated can be used to cut, weld, or mark workpieces.
In addition to the blowback operation described above, alternative known techniques include blow forward technologies, in which the nozzle separates from a stationary nozzle. See, e.g., U.S. Pat. No. 5,994,663, the contents of which are incorporated herein by reference.
Dimensions of the torch are determine by the size and configuration of the consumables discussed above, e.g., the electrode, swirl ring, nozzle, and shield. Design of these consumables is highly technical and has a dramatic impact on torch life and performance. The electrode is generally surrounded by a swirl ring, a nozzle, and in some configurations a shield. All of these components, and the manner in which they are designed and combined, affect the overall torch dimensions, configuration, weight, cost and other parameters.
Furthermore, hand-held torches are now being used in ever more intricate cutting operations, including those where access to portions of the workpiece can be difficult. Standard torches, due to their dimensions, may not be usable in hard to reach areas such as channels and corners. In addition, most hand-held plasma cutting torches have a torch head that is fixed at an angle between about 90° and about 115° relative to the handle. While this configuration is well suited for many cutting applications, it is not ideal for cutting into sharp corners or in pockets and for many gouging applications.
The torch consumables (e.g., the electrode, nozzle, swirl ring and shield) are exposed to high temperatures. Standard torches cannot run at a high percentage duty cycle without melting the torch components and causing other temperature-related problems in the torch. The torch consumables can be cooled utilizing various techniques, such as water injection cooling to cool the nozzle and/or shield, liquid cooling in the electrode and/or about nozzle, or vent holes to cool the shield as described in U.S. Pat. No. 5,132,512, the contents of which are incorporated herein in their entirety. The cooling of plasma arc torch consumables can become even harder when the plasma arc torch is run at high currents (e.g., greater than about 15 Amps) and/or when the plasma arc torch is entirely gas cooled.